Many modern electrical machines are powered by electrical power supply circuits. However, current leaks within a power supply circuit allow electrical current to leak out of the power supply circuit and flow along an unintended path. Leaked current can pool within the structure of an electrical machine and form an electrical charge. When a connection path is made between the structure and an electrical ground sump, hereinafter also referred to as “Earth Ground,” the built up electrical charge is released/discharged as an electrical fault current which flows from the structure, through the connection path, and into the sump. Such fault currents are dangerous as they may damage sensitive electrical components. Moreover, when the connection path passes through an individual, a fault current may cause injuries such as blistering, burns and/or death.
In order to prevent fault current caused by current leaks, many electrical machines and convenience outlets are protected by devices, known as ground fault circuit interrupters (“GFCI”), which interrupt/“shut off” the electrical current of a power supply circuit after a current leak has been detected so that a charge cannot build up within the structure of an electrical machine. Traditional GFCIs detect current leaks by measuring the current leaving one side of a power source (“the hot wire”) at a point just prior to entering the electrical machine and comparing it to the current measured on the return path (“grounded conductor”) at a point just after the electrical machine. Differences between the measured currents indicate current leakage within the electrical machine. As such, traditional GFCIs may require that a protected electrical machine/system be connected to Earth Ground.
Accordingly, traditional GFCIs work well for electrical machines having one or more electrical motors that operate on the same power requirements in which the current flowing into the hot wire(s) of the electrical machine equals the electrical current flowing out of the grounded conductor(s) of the electrical machine. However, there exist many electrical machines which are configured such that they have two or more current carrying conductors and may not be connected to Earth Ground. Accordingly, such machines cannot be protected against fault currents by traditional GFCIs.
Further, there additionally exist machines, known as mixed load machines, which include two or more electrical motors having differing electrical power requirements/loads. For example, a mobile masonry saw may have a primary electrical motor that drives a cutting blade and operates on 240 volts alternating current (“VAC”) and a secondary electrical motor that drives a cooling pump and operates on 120 VAC. In such mixed load electrical machines, it is often the case that the primary motor is powered via two 240 VAC hot wires, the secondary motor is powered by just one of the two 240 VAC hot wires, and the grounded conductor is connected to the secondary motor. Because current imbalances are likely to exist between the two 240 VAC hot wires, traditional GFCIs cannot accurately detect current leaks within the two or more electrical motors. Instead, mixed load electrical machines are often protected against current leaks via grounding wires attached to the structure of the mixed load electrical machine. Such grounding wires allow leaking current to drain away from the structure so that an electrical charge does not build up within the structure. However, grounding wires must be connected to Earth Ground in order to drain leaking current out the structure of a mixed load electrical machine. Accordingly, operators of mixed load electrical machines should verify that the grounding wire is actually grounded to Earth Ground prior to powering up the mixed load electrical machine. However, for various reasons, such as lack of training, time and/or testing equipment, many operators of mixed load electrical machines fail to do so. Additionally, a grounding wire that tested positive as being connected to Earth Ground prior to powering up a mixed load electrical machine may subsequently become compromised, without warning, such that it looses its connection to Earth Ground during operation of the mixed load electrical machine.
With the foregoing concerns in mind, it an object of the present invention to provide for an improved GFCI that is capable of detecting current leaks within an electrical machine that does not require a grounding wire. It is another object of the present invention to provide for an improved GFCI that can detect current leaks within mixed load electrical machines.